1. Field of the Invention
This invention generally relates to a linear motion guide unit, and, in particular, to a finite linear motion guide unit having a rack and pinion mechanism.
2. Description of the Prior Art
A finite linear motion guide unit having a rack and pinion structure is known and a typical prior art example is described in the U.S. Pat. No. 3,857,618 issued to Hagen et al. on Dec. 31, 1974. However, in the structure shown in this patent, since pinions are provided on both sides of a retainer in pairs, the meshing condition between the pinions and the associated racks may differ between left and right when the retainer is deformed due to some external forces, whereby a resistance against movement could be increased. Moreover, since the pinions are provided in pairs arranged side-by-side, the overall structure tends to be large and bulky so that there is a limit in making a linear motion guide unit compact in size. Besides, the linear motion guide unit shown in this patent is extremely complicated in structure and thus the manufacturing cost tends to be high. As a result, it was not possible to apply this type of linear motion guide unit to high precision devices, such as a head guide unit of a hard disc drive and a guide unit of a precision measuring apparatus.